The present invention relates to the marking of industrial parts. In particular, the invention relates to permanent marking of parts used in hostile environments and where physical alteration of the part to create the mark can be detrimental.
In many industries, it is necessary to identify and track the individual component parts of a machine or device. For example, in the manufacture of aircraft engines or gas turbines, the individual airfoils comprising the turbine must be tracked during the life of the engine or turbine. Part marking allows a manufacturer to track parts during the component""s life cycle. Thereby, long-term data is collected for reliability modeling, future design improvements, and contract compliance. The markings on a part can be adversely affected by the severe environments within the turbine hot gas path and by the cleaning/repair operations encountered during periodic maintenance operations.
Ideally, such markings are permanent, able to withstand usage (e.g., surface abrasion), able to withstand thermal cycling, able to withstand harsh environments during use and servicing, and, most importantly, have no impact on the function and lifespan of the part. Certain parts additionally require that their mechanical design not be compromised by the creation of markings upon the surface of the finished part. The removal/displacement of a part""s material can affect the function of a system (weight distribution and balance can be affected) or can endanger the part itself (stamped lettering can act as an initiation site for stress cracking).
Part marks can be of two types: human readable and non-human readable. An example of the first is a string of letters and numbers written in a particular size and font. An example of the latter is a supermarket barcode.
A number of part identification approaches have been tried with varying degrees of success in durability and readability. Inks and paints have been used to identify parts with bar-coding or simple character information. Such markings may be referred to as two-dimensional (2D) in that they substantially only affect two dimensions of the surface of the part. These methods are insufficiently permanent under the thermal environments typically encountered in aviation or power generation. Labels applied to the part surface wear off or burn off and are unsuitable for parts where the surface area is uneven or lacking sufficient area to be readable. Metallic labels are hazardous when dislodged, difficult to remark in the field, and weighty by comparison to other marking types.
In order to track a part over its lifetime, the markings must be read and input into a computer system at every point of handling. Recognition accuracy often must exceed 99.99% in order for reliable life data to be accumulated. Humans cannot usually reach these levels for any significant amount of time. Machine systems which read the part markings and directly input the data into the computer system must be applied to approach the reliability required.
For the forgoing reasons, there is a need for an apparatus and simple system of part marking that is easily readable in the field yet requires no modifications to the surface of the part such as cutting, etching, abrading, laser or other form of removal of material.
The invention disclosed herein consists of a system of modifying the physical properties of the materials comprising the surface of the part or a subsurface zone extending some depth into the material at specific localized sites using physical means that do not affect the strength related or 3D characteristics of the part material and do not rely upon painted or other 2D marking being applied to the part surface.